Write a solution to find the second highest salary from the Employee table. If there is no second highest salary, return null (return None in Pandas)

Sure, here is a solution using SQL:

SELECT MAX(Salary) AS SecondHighestSalary
FROM Employee
WHERE Salary < (SELECT MAX(Salary) FROM Employee)

This query works by first finding the maximum salary in the Employee table. It then finds the maximum salary that is less than this value, which is the second highest salary.

If you want to do the same in Python using pandas, you can use the following code:

def second_highest_salary(df):
    sorted_salaries = df['Salary'].sort_values(ascending=False).unique()
    if len(sorted_salaries) < 2:
        return None
    else:
        return sorted_salaries[1]

This function sorts the 'Salary' column in descending order and removes duplicates. If there is no second highest salary (i.e., all employees have the same salary), it returns None. Otherwise, it returns the second highest salary.